In the case of reinforced concrete frames, full moment redistribution may not take place, and any critical regions may fail because of insufficient rotation capacity before a collapse mechanism is formed. Considering the limited rotation capacity of concrete sections, a method is developed to verify and analyze the identified dominant mechanisms that are impossible to form. A reliability model for the rotation failure prior to mechanism collapse is proposed, and the safety margin equation, in relation to and consistent with the mechanism, is generated on the basis of the partial utilization of moment redistribution at the failure stage. Rotation failure modes are combined with other possible mechanism modes, and the structural reliability is reassessed. The proposed method is illustrated with two examples. It is found that a check of plastic hinge rotations and remodeling of the failure modes improve the accuracy of predicting the system reliability of a reinforced concrete frame. However, the improvement is only marginal in the case of simple frames.